Electric signaling system



Jan. 12 1926.

R. D. CONWAY ELECTRIC SIGNALING SYSTEM Ray D. (o/May Jan. 12 1926.

R. D. CONWAY ELECTRIC SIGNALING SYSTEM Original Filed t. 7. 1921 5 Sheets-Sheet 4 NNN Mrcnfar: fay C anu ay y Q I HHHH %\h 4 I l I I QM Rm J LIP... Nxfi QM "H H H m? H m C WY 8 p p \N wGwQ E W Q GWMM \lhm w 3% g RN Rm M W g X. i nw a M k .NKQQ\Q m U mmfi wk v Jan. 12 Q 1926.

R. D. CONWAY ELECTRIC SIGNALING SYSTEM 5 Sheets-Sheet '5 Original Filed 001;- 7. 1921 Patented Jan. 12, 1926.

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rarer BOY D. CONW'AY, OF BASKING RIDGE, I-TE'W JERSEY, ASSIiGNOR TO WESTERN ELEC- TRIO COMPANY,INCORPOBATED, OF NEW YUEK, Null, A C-QBIL ORATION OF NEW YORK.

ELECTRIC SIGNALING SYSTEM.

Application filed October 7, 1821, Serial No. 506,085.. Renewed June 20, 1925.

To aZZ 10. 2.022 it may concern.

Be it known that I, ROY D. CONWAY, a citizen of the United States, residing at Basking Ridge, in the county of Somerset, State of New Jersey, have invented certain new and useful Improvements in Electric Signaling Systems, of which the tollowing is a full, clear, concise, and exact description.

This invention relates to systems of electric communication, wherein two stations are interconnected by a trunk line which may be seized by any one of a plurality of lines terminating at one of said stations.

The object of the invention is to provide in a system of this character a simplified circuit arrangement whereby the identity of the line which has seized the trunk is indicated to an operator at the other station where the distant end of the trunk terminates. I p

, The invention is particularly applicable tO-SBlViC6 ObSeIVl11g systems for telephone exchanges, wherein a service observing trunk extends from each of the oltices of the exchange area to a central observing point where the observers are located, but is not to be considered as limitedto such systems. in systems of this character a certain number of lines of a given exchange are temporarily associated with the service observing trunk, and when one of these lines initiates a call, the usual line lampbe'fore the regular operator lights, and in addition, a lamp at the observing office is also lighted over a circuit including the service observing trunk. The observer then actuates a key to connect herhead set to the trunk and to prepare a circuit which is closedto light another lamp when the subscribefs operator plugs in to answer the call. When the subscribers operator has set up the connection, she operates a message register key to advance the line meter to register the call, or it the line is a pay tation line, operates a coin collect or coin refund key. The actuation of the particular key causesa signal to be given to the observer at the distant point. The position oi the subscribefis switchhook of the line under observation is also indi- .cate d bv signals at the observers desk.

When Q plea-ri p rator has finished.

observing the character of service, she opcrates a key to cause the apparatus at her position to indicate toher the number of the subscribers line under observation. The c rcuits for operating the aforementioned Signals and the indicating apparatus include the service observing trunk. This trunk is also used to operate a guard signal to inform the operator when she dis-con nects her head set from the service observing trunk without actuating her release key to disconnect the line under observation from the-service observing trunk.

in the circuit arrangement of this invention, all'these functions are performed over a trunk consisting of only two conductors interconnecting the oiiice where the subscribers lines terminate, and the service observing ofiice.

This invention will be more readily understood by reference to the accompanying drawings.

Referring to the drawings, Fig. 1 shows a pair of subscribersl lines and a cord circuit; Figs. 2 and 3 show that part of the service observing/trunk which is located at the oflice X whereinthe subscribers lines shown, terminate; Fig.4 shows that partof the service observing trunk which terminates at the distant office where the observers are located, Fig. 5 shows a modified form or the invention; Fig. 6 shows another modification; Fig. 7 is a simplified diagram of the VVheatstone bridge at .o'liice X, and Fig. 8 is a simplified diagram of the VVheatstone bridge at office Y.

As shown in the drawings, this invention comprises a service observing trunk D, oi? only two wires extending between central otlices X and Y. At central oflice X a plurality of telephone lines terminates, two of whica are shown in Fig. 1; lnFig. l is also shown an ordinary cord circuit E, for connecting the telephone lines for conversation. lirFig. 2 there is showuthe end of the service observing trunk D, which ter minates'in central cities 31. As shown in Fig. 4:, theend of the service observing trunk D at central oilice Y'terminates in a posi tion of a service observing desk. Associated with the service observing trunkD is apparatus tor indicat ng o the per t t the service observing desk, the number of the line upon which service is being observed. The indicating apparatus'which is located on the service observing desk is shown in Fig. 4. 1

A service observing system embodying this invention is capable of use for observing the service upon any one of at least ten telephone lines. For convenience, however, only the first and last telephone lines, #1

. and #10, are shown in the drawings. Tele- ,sponding to the number phone line #1 is equipped at the substation with a coin collector, while telephone line central office with a Telephone line #1 is connected to jacks 139 and 140by means plugs 2 1; and 25, and telephone line #10 to jacks 14:1 and 142 by means of plugs 27 and 23. Associated with the service observing trunk D at central oflice X, are three relays #10 is equipped at the message reglster 32.

incividual to each telephone line to which 7 D has access the service observing trunk for connecting the trunk to thetelephone line upon which a call is being'made. Re lays 109, 113 and 11 1 are individual to telephone line #1, and relays 110, 116 and 143 are individual to telephoneline #10. The leads from jack 139 terminate in nor mally open contacts of relay 113. Thelead from the upper contact of jack 1 10 terminates in a 11 1, and the lead from the lower contact 140 extends through resistance 151, and the .vinding of relay 101 to battery. The leads from jacks 141, 142 are similarly associated with relays 1 13, 116 and 110.

at the service observing desk there is a lamp corresponding to each ofthe ten telephone lines to which the service observing trunk D has access. Forconvenience, these lamps are given numbers- 301 to 310, correof lines 1 to 10. At the operators position of the service observing desk, there is an indicating key 2170011- trolling the indicating apparatus. Key 206 serves to connect the position apparatus with. the serviceobserving' trunk D and the telephone line connected with it, while key 219 is for the purpose of releasing the service observing trunk from a connected telephone line. 1

The subscriber of telephone line #1, initiating a call, removes the receiver from the switehhook, and deposits a coin 29 inthe coin box. Belay 15 thereupon operates over a circuit :t'roni battery, relay 15, contact of cut-oil relay 17, tip side of the line, windings o1 electroinagnet 30, and coin host, to ground. Armature 31 of electromagnet 30' is unafi'ected by the establishment of this circuit. The operation of line relay 15 lights line lamp 16 and causes the operation of relay 101 over a circuit from battery, relay 101, resistance 151, sleeves of the jack 140 and plug. 25', contact of line renormally open contact of relayv cuit from the coinv 29 in the,

lay 15, to ground. The operation of relay 101 causes the operation of relay 102 over a circuit from battery, relay 102, inner normal contact of relay 104, contact ot relay 101, and normal contact of relay 105, to ground. The operation of relay 102 causes the operation of-relay 135 over a circuit-from battery, relay 135, outer contact of to ground. The operation of relay 135 *auses the operation of relay 201 over a oir cuit from battery, normal contacts ofkeys 217 and 219, relays 212, 201, retard coil 203, tip side T 01 the trunk including outer normal contact oi relay 202, 'norinal contact of ielay 10S, retardation coil 106, contact of relay 135, low resistance winding of relay 100, ground. Relay 201 in operating lights larnp20? to indicate that a call is being made on one of the telephone lines to which the service observing trunk D has access.

The operation of relay 102also causes the operation of relays 109 and 110 over a circuit from battery, relay 110, the Winding of relays corresponding torelay 110 individual to other intermediate lines under observation and relay 1'09, inner contact of relay 102, and normal contact ofrelay 112, to ground. Re lay 109 in operating causes the operation or relays 113 and 11 1. Relays 113 and 114 operate over a circuitt'rorn battery, contactof relay 109, sleeves of jack140 and plug 25, and the contact of line relay 15, to ground. The operation of relay 113 limbs of telephone line #lto ring conductors of the service observing trunk. The operation of the relay 114 causesthe operation of relay 112 over a cirbattery, relay 112, middle contact 01" relay 114, sleeves of jack 14:0 and plug 25, and the contact of line" relay 15, to ground. 112 causes the release otrelays 109 and 110. Relays 113 and 11 1, upon operating, are locked from battery, through the windings 01'' these two relays, the innermost alternate contact of relay 113, then through the winding 105 and outer normal contact of relay 10 1, to ground. Relay 1.05 operates, causing the release of relay 102, and as long as relay 105 is operated, all other telephone lines to which this service observing trunk has access are prevented from being connected thereto because the energizingcircuit of relay 102 is open at the normal contact oi" relay 105. The release of relay 102 does not cause lamp 207 to be extinguished, tor the operation oi relay 112 already referred to, has furnished ground for maintaining relay 135, and consequently relay 201 operated.- Assuming that the lighted condition of lamp 207 is observed by the operator at the service ohserving: desk, this observer actue'ieslistening key 206. Signal lamp'20'2' is responsive to the position of the connected subscrihers witchhook, as will be more tally explainedthe tip and relay 102,

connects the y l of relay later. The operation or this key 206 connects the observers telephone 221 to the service observing trunk l).

Then the regular operator, upon noticing the lighted condition of the' line lamp 16,

answers by inserting the answering plugol the cord circuit E into the jack associated with the telephone line #1, cut-0E relay 17 and relay 117 operate over a circuit from battery, through lamp 18, resistance 19, sleeve of the answering plug and'jack to point 20, where it branches, one branch going throughthe winding of cut-oil relay 17, and the other through the tip contacts 0t plug 25 and jack 140, the innermost contact of relay 114, relays 117 and 118, to ground. Relay 118 is. marginal and does not now operate. The operation of cutoff relay 17 releases line relay 15, extinguishing line lamp 16, and releases relay 112. The operation ofi'elay 117 causes relays 119 and 120 to operate in parallel over a circuit from'battery, through the contact of relay 117, normal contact of relay 121, right normal contact of relay 119, windings of relays 119 and 120 in parallel, and outer normal contact 01 relay 104, to ground. The operation of relay 120 extends the tip and ring conductors of the service observing trunk to which are connected the limbs of tele: phone line #1, through to the service observing desk. The operation of relay 117 also causes theoperation of relay 122 over a circuit from battery, through the contact of relay 11 and the winding of relay 122 to'ground. The operation 01 relay 122 by shunting out resistance 175 causes the operation of marginal relay 208 over acircuit from battery, through a contact or" key 206, now actuated, windings or relays 230, 208, coil. 209, ringside/R- oi thetrunk including right inner normal contact ot'relay202, left inner normal contact of relay 108, coil 124, inner right contact of relay 122, contact of relay 118. relay 103, to ground. Relay 208 in operating causes the lighting of lamp 210, which indicates to the observer that the regular operator has answered the call. The operation of relay 122 also connects battery through its left contact to avoltmeter relay 120, shown within the dotted lines of Fig. 3,

and completes a VVheatstone bridge circuit in which resistance 127 forms the first lined. arm, resistance 128 the second fixed arm, resistance 21 and lamp 18 in parallel. and in series with resistance 19, forn'iing a third arm, and the fourth arm consisting of four branches in parallel, the windingot cut-oil relay 17. beingthe first, the windings of relays 117 and 118 in series being the second, resistancej12t) being the third, and resistance 130 the fourth. This VVheatstone bridge is shown in simplified form in Fig. 7 with the parts correspondingly numbered.

.A moving coil 1311s connected across this -tery.

the release of relay 112. Lamp 207 thus" remains lighted to indicate to theobserver that the subscriber has the receiver oil the switchhook. the receiver to the switchhook, supervisory relay 22 releases, removing resistance 21 from parallel relation to lamp 18, thereby.

changing the resistance of the third arm of the bridge to such an extent that the bridge becomes balanced. The coil 131 then assumes its ormal. position, opening contact 182, which releases relay 135. Relay 201: thereupon releases, extinguishing lamp 207, thereby indicating to the. observer that the subscriber has restored the, receiverto the switchhook. p I i Upon connection being completed be-. tween the calling telephone line #1 and the When the subscriber restores called telephone line, the regular operator.

by actuating coin collect key 33-causes the coin 29 to be deposited in a proper receptacle. This is accomplished in the following manner. The actuation of key 33 causes the energization of electromagnet 30 over. a circuit from negative battery 34, through winding of relay 36, upper alternate con tact of key 33, upper normal contact-of key 41, tip contacts of the answeringplug and jack, winding of electromagnet. 30-and coin 29, to ground. Upon the energization of electromagnet 30, armature 31 is moved about its pivot pointto close its lower contact and in so doing causes the deposit of the coin 29 into a suitable receptacle in any well known manner, as shown for example in Patent 1,043,219 to O. F. Fo-rsberg, issued November 5, 1912. The closure or the lower Contact locks up the electromagnet 30 as long as key 3?) remains actuated The closure of the circuit from negative battery 34 operates relay 36 to cause the lighting of pilot signal 37. Negative battery 34 and positive battery 38 are of higher volt age than the common battery at the central o'tlice, being preferably of volts, while the voltage of the ordinary central oflice battery is preferably 24. The actuation of key 33 also causes the operation of relay 155 over a circuit from negative battery 34, through the winding of relay 36, upper alternate contact of key 33, upper normal contact of key 41,.tippontacts of the answering cuit from about" polarized relays 156 and 153, whereupon polarized relay 153 operates. Polarized relay 153 operates on negative battery from 34, but does not operate on positive battery from, 38, while polarized relay 156 operates on positive battery from 38 but does not operate on negative battery from 34. Relay 155 in operating also causes the operation of relay 157 over a circuit from battery, through the winding of relay 157 and the alternate contact of relay 155, to ground. The operation of polarized relay 153 and relay 157 completes a tone circuit from the source of tone current produced by the interruption of the circuit from battery through interrupter 158 and coil 165 to ground, which may be traced through condenser 163, contact of relay 153, alternate contact of relay 157, alternate contact of relay 160, repeating coil 159, relay 108, to battery. Aninterrupted flow of current in this circuit causes in the secondary of repeating coil 159 an induced flow of current, which traverses the primary Winding of repeating coil222, whereupon current will be.

induced in the secondary thereof. The path of the induced flow of current in the secondary of repeating coil 222 includes the receiver of the observers telephone 221. In this manner the observer receives a distinctive signal when'the regular operator collects the coin. The release of the coin collect key 33 by the regular operator permits relays 153, 155 and 157 to release, whereupon the tone to the observer ceases. In a similar. manner, theobserver receives a tone when the regular operator refunds a coin, as in the case where the calling subscriber does not obtain connection with a definite line called for. Coin refund key 41, is operated to apply positive current when the regular operator refunds the coin, whereupon relay 40 operates to light the pilot signal 37. The electromagnet 30 being energized, moves armature 31 about its pivot point to close its upper contact, and in so doing refunds the coin to the subscriber in any well known manner. Relay 155 also operates, permit ting polarized relay 156 to operate and causing the operation of relay 157. Interrupter 161, instead 015158, will thereupon be included in circuit with battery and primary of repeating coil 159. The number of segments on interrupters 158 and 161 being different, the observer receives tones of different character and. is thereby enabled to determine by these different tones when the, regular operator collects or refunds a coin.

Suppose that a call is made on telephone line Theoperutionfolf line relay 42 of this line in addition to lighting theline lamp, causes the operation of relay 101, which in turn will cause th operation of relay 102. Relay 102 in operating causes the operation of relays 109 and 110, and the operation of the latter relay completes a cirsuit for relays 143 and 116 to ground at the front Contact of linerelay 42. Relay 143 in operating eonnectsthe limbs of telephone line #10 to the tip and ring conductors of the service observing trunk, and relay 143 in operating completes a locking circuit for-relays 143,116 and 105 to ground. at the back contact of relay 104. The operation of re lay 102 causes the operation of relay 135, which causes the operation of relays 201 and 212. Relay201 in operating lights lamp- 207 Up to this point the circuits function i in the same manner as described in connection with line #1. Assuming that the ob; server has noted the lighted condition of lamp 207, shefactuates key 206, which operatesfrelays 103, 208 and 230. s The observers telephone 221 will also be connected to the tip and ring conductors ,ofthe service observing trunk. The regular operator, noting the hghte'd cond tion of the line lamp,

7 now answers in the usualmanner by inserting the answering plug into the jack asso ciated with line #10, whereupon the cut-off relay 43 and relay 117 operate. Relay 118 is marginal and does not operate at this time. The operation of relay 117 causes the operation' of relays 120, 119and 122. Relay 122 connects battery to the volt meter relay 126. Since telephone line #10 is a' message'register line, the fourth arm of the theatstone bridge o f the voltmeter relay will the same as in the case of linettl,

except that the resistance 129 willbe replaced by the windings of the, meter 32. It is to be noted that this fourth arm of the bridge.

in thecase of a telephone line equipped with a message register eontains the winding of the electromagnet of the message register, while in the case of a line not equipped with a message register], the message register winding is replaced by a resistance 129.

When th subscriber on telephone line #10 has been connected to a called line, the regu lar operator registers the call on the message register 32 by the actuation of a key 35. This is acconiplishedby establishingthe 'lel lowing circuit upon the actuation of key 3.5, battery44, preferably 39 volts, through position register 45, contact 46 of key 35, sleeve contacts of answering plug and jack, both windings of electromagnet 32 in series of the line register to ground. The line regis;

ter32 and position register 45 are energized,

attracting their armatures to cause the regis tration of the call. When the armature, of electromagnet 32 is attracted, the right winding thereof is' short circuited. This magnet will remain energized from the central office battery after the release of key When the electromagnet of the position register 45 and the electromagnet 32 of the line register were energized, marginal relay 118 was operated over a circuit from battery 44, through the winding of the electromagnet of position register 45, contact 46 of key 35, sic-eve contacts of the answering plug and jack, upper engaged contacts of plug 28 and ack 142, inner contact of relay 116, and windings of relays 117, 118, to ground. Relay 118 is responsive to a flow of current from a 39 volt battery, but is not responsive to a flow of current from the regular central ofiice battery of 24 volts. Relay 118 in operating causes the release of relays 230 and 208. Relay 230 releasing, lights lamp 236 and operates bell 231. The lighting of the lamp and the operation of the bell indicate to the observer that the regular operator has registered a call on the message register line, which is connected to the service observing trunk. The release of key 33 by the regular operator releases relay 118, which reoperates relays 230 and 208, whereupon lamp 236 is extinguished and buzzer 233 ceases to operate.

The voltmeter relay 126 operates in the same manner as hereinbefore described in connection with a call on telephone line #1, and causes the signal lamp 207 to indicate the position of the subscribers switchhook to the observer. Lamp 210 was lighted when the regular operator plugged in to answer the call to indicate this fact to the observer.

lVhen the operator desires to ascertain the number of the line under observation, she depresses indicating key 217. This opens the upper or tip side of the trunk, releasing relay 160. Relay 160 in releasing energizes relay 108 over a circuit from ground on front contact of relay 105. RC".

lay 108 locks to the. normal contact of relay 137. The operation of key 217 releases relay 216, which operates relay 202. Relay 202 applies high potential positive current to point 311 of the Wheatstone bridge 312, and operates relay 313. Resistances in arm 3197are equal to resistance 147 of line #10 and resistance 148 of line #1 plus the resistances of the intermediate lines, all of which are not shown. Resistances 321 and 322 being equal, and resistance 149 now connected in series with the tip of the trunk through the outer left contact of relay 108 being equal to resistance 150 now connected in series with the ring of the trunk, through the inner left contact of relay 108, and since resistances in arm 319 are short circuited by the normal contacts of relays 316, 318

and 320, and resistances 147 and 148, etc.

.114, assuming line #1 is under observation,

321, 150, 148, and through marginal polarized relay 137 is not of sufficient strength to operate relay 137. Therefore, ground from contact of voltmeter relay 312, through the winding of relay 314 operates it, removin battery from conductor 317, preventing the operation of relay 316. Current flowing over conductor 315 from battery through the contact of relay 313 therefore lights lamp 301, indicating to the observer that line #1 is the. line that is under observation. This l/Vheatstone bridge is shown in simplified form in Fig. 8 where the parts are correspondingly numbered.

Assuming that line #10 is being observed, and the observer wishes to ascertain the number of the line, she depresses indicating key 217. Then when relay 202 applies current from the positive. high potential battery through the winding of relay 313 to point 311 of the W'heatstone bridge, volt-' meter relay 312 will operate due to an unbalance, since the resistances 147 and 148, etc. are included in the circuit in series with resistance 150. Relay 312 in operating prevents the operation of relay 314, and current flows from battery through the. contact of relay 313, the contact of relay 314 to lead 317, and operates relay 316. Relay 316 in attracting its outer left armature removes a short circuit from around part of the resistance 319, which corresponds to the part of the resistance associated with line 2. This does not balance the bridge, and voltmeter relay 312 remains operated. When relay 316 attracts its inner left armature it opens the circuit of lamp 301. In attracting its rightarmature it locks by wayof conductor 315 to battery at the alternate contact of relay 313. In attracting its inner left armature, I

operated. Relay 318 in attracting its right armature locks to ground at the alternate contact of the left inner armature of relay 316. In attracting its inner left armature it opens thecircuit of lamp 302. The other relays similar to relays 316 and 318, notv shown, operate, removing the short circuits c from around other portions of resistance are short circuited by the contact of relay 310, and lock up, until a circuit is extended from ground at the left mner armature of reiay 316 to the winding of relay 320, which operates and removes the short circuit from around the remaining portion of resistance 319, corresponding to resistance 148. This balances the circuit of the Wheatstone bridge, releasing the voltmeter relay 312, operating relay 31 1, and lighting lamp 310. Relay 320 in attracting its right armature locks up to conductor 315 and to ground at that the observing operator has a list showing this relation. in this manner when a particular indicating lamp 301 to 310 lights, the number can be immediately associated with the actual number of the line being observed.

In order to disconnect the telephone line under observation from the service observing trunk, the operator actuates release key 219, which opens the circuit of slow relay 216. Relay .216 in releasing operates relay 202. fhe depression of key 219 releases relay 160, whereupon relay 108 operates from the ground on the armature of relay 105, and locks to the armature of relay 137. Relay 216 is made slow to release to give relay 160 time. to release and operate relay 108 before relay 216-by closing its back contact operates relay 202 to apply current from battery 110 volts to the trunk. This current would otherwise hold relay 160 operated and thus prevent the operation of relay 108 to connect relay 137 to the trunk. clay 108 in operating disconnects rela 160 from the trunk. Relay 108 at its is .t arn'uiture connests the relay 137 to the tip and ring of the trunk. The connection to the tip leads by way of resistance 1&9 and the outer left armature of 108 and the connection to the ring by way of 17, l i-8 and 150 and the inner lei-t armature of relay 108. jtelay 202 applies high potential positive current to both sides of the. trunk in parallel through contacts of key 219 of sufiicient strength to operate polarized relay 137 to close its lower contact, which closes a circuit for relay128, extending over the left alternate contact of relay 119, to ground on the armature of relay 105. Relay 128 looks independent of relay 105 and also operates relay 104:. Relay 10 1 in operating, releases relays 105, 113' and 114:, disconnecting the service observing trunk from line #1. l; hen the operator restores the key 219, low potential negative battery is connected to the upper side of the trunk by way of normal contacts of keys 219 and 217, to cause the polarized of relays 112 t10n of lamp 207 notifies the observer that 'tuated before the to answer, relays 121 and 162 will be reesse relay 137 to open its lower contact and operate its upper contact to release relay 108.. Relay 108 1n releas ng disconnects relay 137" from the trunk D. Relays 110'and 120 release when relay 104 operates. Relays 310 to 320 are restored to normal due to the release of relay 313 which becomes inert when relay 202 releases due to slow relay 216 becoming energized when the operator restores her release key. The release of relay 320 extinguishes lamp 2310.

Assuming now that after the lamp 207 is, lighted due to a call having been made on telephoneline #1, key 206 at the service ob serving desk is not actuated. The operation of relay 105, heretofore referred to, would cause the operaton of relays 121 and 162.

The operation of these relays brings about" the following results: {1). inakesit possible 3 for the service observlng trunk to be released automatically by a regular operator when plugging in to answer, provided the observer has not taken up. the call; (2) provides a guard signal to warn the observer in case the position apparatus at the service observing desk has been disconnected from the trunk circuit without releasing the trunk circuit; and (3) furnishes a guard signal to the observer in case the subscriber takes the receiveroff the switchhook, thus connecting and locking the telephone line to the service observing trunk, and then restores the receiver to the switchhook before the regular operator answers by plugging in. This guard signal notifies the observer that the trunk clrcult shou d be released Referring to function #1, relays 121 and 162 operate over the following circuit when relay operates: ground, alternate contact of relay 105, relay 162,, battery. A circuit parallel with relay 162 leads over the left normal contact of relay 119, relay 121, con tact of relay 103, battery. Relay 162 in operating connects ground to relays 2132 and 201 through the high resistancewinding of relay 1.60so that if relay 135 releases, denoting that the subscriber has hung up, relay 201 releases while relay 212 is J'Dfillllifillltl operated and lamp 230 will light. Lamp 20? is lighted due to the operated condition and 201. The lighted condithe telephone line on which a call has been,

made has been locked on to; the service ob. serving trunk, as already described. If the key 206 of the service observing desk is acregular operator plugs in leased, due to the opcratioir of relay .103

when key 2061 s operated, as described, so

that upon the subsetpient plu 'ing in by the regular-operator, lamp 210 will be lighted' to apprise the observer regular operator plugs of this fact. If the in to answer before the observer takes up the call by actuating .key 206) the operated condition of relay 121.

I 117, alternate contact of relay 121, and winding of relay 104 .to ground. Relay 104 in operating, releases relays 105, 113 and 114, thereby disconnecting the service observing trunk from telephone line #1, upon which a call was made. ,All apparatus associated with the service observing trunk thereupon returns to normal condition, ready to connect the service observing trunk to another telephone line to which the trunk has access when a call is made. Function #1 of the circuit through relays 121 and 162 is thereby accomplished.

WVith reference to function #2 above referred to, if the observer after completing an observation on telephone line #1 disconnects the position apparatus by restoring key 206 to normal positionwithout releasing the trunk circuit by actuating release key 219, lamp 239 will be lighted to warn the observer that the trunk circuit has not been released, as previously described.

As to function #3 of the circuit, including relays 121 and 162, the making of a call on telephone line #1 causes the lighting of lamp 207 and locks the telephone line to the service observing trunk (as hereinbefore explained), but if the subscriber on telephone line #1 restores the receiver to the switchhook before the regular operator answers by plugging in and before the observer takes up the call, relay 112 will release, causing the lamp 207 to be extinguished. Lamp 239 will light to notify the observer that the service observing trunk should be released.

Relay 137 is marginal and polarized. It is marginal so as not to operate to close its lower contact on 110 volt positive current applied by relay 202 through relay. 313 to the bridge. hen release key 219 and relay 202 apply 110 volt positive current directly to the tip and ring of the trunk, relay13'7 operates to close its lower contact to operate relay 128, as described. When key 219v is restored negative current is applied to operate relay 137 to close its upper contact to release relay 108.

Instead .of employing the counting relays 316, 318, etc. of Fig. 4, a motor-operated rheostat, such'as shown in Fig. 5, may be used. Conductors 330, 331 and 332 of Fig. 4 are connected in Fig. 5 to the l/Vheatstone bridge shown in this figure similarlyto the manner in which they are connected to the VVheatstone bridge of Fig. 4. In this modification when the operator 'actuates the indicatiug key 2170f 4, relay 216releases and operates relay 202 to apply positive current to point 511 (Fig. 5). Assuming line #10 to be under observation, the moving coil 500 causes its contact arm 5.12 to close its lower contact, operating relay 550 which closes the circuit of the field winding 551' of the motor and also closes a circuit for the armature winding 552, this latter circuit including the normal right contact of relay 553 and the inner left normal contact of this relay. The closure of these circuits causes the motor to rotate the screw-operated shaft 554 to move the contact brushes and 556, mounted upon but insulated from screw 554, downwardly. When the bridge becomes balanced, contact arm 512 moves to its neutral position, releasing relay 550 which opens the circuits of the motor, stopping the shaft with brushes 555 and 556 engaging the lowermost segments 557, 558, respectively, in-

cluding the entire resistance in the arm 519 of the bridge in circuit with conductor 332.

Lamp 510 thereupon remains lighted to indicate to the observer that line #10 is the line under observation. The bars 561 and 562 are made up of segments such as 557, 558 insulated from each other. The bars 563, 564 are continuous metal bars.

If the line under observation is line #1 the moving coil 500 closes spring 512 to its upper contact, operating relay 553. This relay at its outer left armature closes thecircuit of the field winding 551 of the motor and at its right armature closes a circuit through the armature winding 552, so that current flows therein in the opposite direction to that flowing when relay 550 operated, whereupon the motor moves the brushes 555, 556 upwardly, short circuiting sections of resistance 519 until a balance is reached, which, since line #1 is under observation, will occur when brushes 555, 556 reach the uppermost segments 559, 560, short circuiting the entire resistance 519. Lamp 501 will then remain steadily lighted to indicate to. the operator that line #1 is under observation.

It will be readily apparent from the foregoing, without further description, that this arrangement will indicate the number of any of the other lines under observation. The resistance 147, 148, etc. connected in the conductors 331,332 determines where the motor-operated rheostat will come to rest and consequentlywhich lamp will stay lighted, and these resistances, as has been explained, correspond to the lines under observation.

. Fig. 6 shows a further modification in which instead of employing a VVheatstone bridge arrangement as in Figs. 4 and 5, a differential relay arrangement is used. The conductors 330, 331, 332 of Fig. 4 are shown connected to the differential relay 650 and to a manually adjustable rheostat 651 in the following manner.

Conductor 330 is connected to the left terminal of each of the windings 621, 622 of relay 650. Jonductor 331 is connected to the other terminal of winding 621 and conductor 332 is connected through-valuable resistance 619 to the other terminal OffWlllCllilQ; 622. In the operation of this modification when the observer actuates indicating key 217 of Fig. 4, relay 216 releases and operates relay 202 to apply positive current to point 652. The observer now rotates the rheostat. arm 653 until one of the lamps 601 to 610 lights which will occur when the arm 619 reaches such a point on resistance 619 as to cause the current flow in the path including such sistance winding 622 and resistance 14:9 to be equal to that flowing in the path including winding 621, the subscribers variable resistance 14-7, 1 1-8, etc, and resistance 150. hen these circuits are balanced the differential relay 650 releases, applying ground to segment 654: which causes the lighting of one of the lamps 601 to 610 to which arm 653 is at the time connected.

From the several embodiments shown it is apparent that the invention may be carried out in a number of different ways and is not to be limited to any of the embodiments shown but only by the appended claims.

What is claimed is:

1. In a signaling system, a plurality of lines, a second station, a trunk circuit consisting of two metallic conductors only interconnecting said stations, means for connecting one of said lines to said trunk, signaling devices at the second station, one for each of said lines, and a circuit arrangement in volving a lVheatstone bridge adapted to cause the operation of the signaling device corresponding to the line connected to the trunk circui 2. In a signaling system, a plurality of lines, a station wherein said lines terminate, a second station, a trunk circuit interconnecting said stations, means for connecting one of said lines to'said trunk, signaling devices at the second station, one foreach of said lines, and a circuit arrangement involving a rVheatstone bridge adapted to cause the operation of the signaling device corresponding to the line connected to the trunk circuit.

3. In a signaling system, a plurality of lines,a station wherein said lines terminate,

V a second station, a trunk circuit interconnecting said stat-ions, means for connecting one of said lines to said trunk, a signal at the second station operated thereby, signaling devices at the second station, one for each of said lines, apparatus involving a Wheatstone bridge adapted to cause the operation of the signaling device corresponda station wherein said lines terminate,

ing to the line connected to the trunk Cir cult, and means actuated by the operator at the second station in response to said signal to cause the operation of said apparatus.

4.111 a signaling system, a plurality of lines, a station wherein said lines terminate, a second station, trunk circuit interconnecting said stations, means automatically operated when one of said lines is taken for response to said signal to cause the operation of said apparatus. 7

In a signaling system, a plurality oi lines, a station wherein said lines terminate, a second station, atrunk circuit consisting of two metallic conductors only interconnecting said stations, means automatically operated when one of said lines is taken for use to connect the same to said trunk and for locking out the remaining lines, signaling devices at the second station, one for each of said lines, and a circuit arrangement in.- volving a \Vheatstone bridge adapted to cause the operation of the signaling device corresponding to the line connected to the trunk circuit. 3

6. In a signaling system, a plurality of lines, astation wherein said lines terminate,

asecond station, a trunk circuit interconnecting said stations, means for connecting one of said lines to saidtrunk, signaling devices at the second station, one for each 'of said lines, a circuit arrangement involving a Wheatstone.bridgeof which two of the arms are fixedresistances, the'thiid arm a resistance varied according to which. line is connected to'tlre trunk, and the fourth arm is a variable resistance, means for automatically adjusting said variable resistance in accordance withthe line connected with said trunk, and means responsive to the setting of said adjusting means for actuating a correspond ing 'one of said signals. v V 7. In a signaling system, a plurality of lines, a station wherein said lines terminate,

a second station, a trunk circuit consisting of two metallic conductors only interconnecting said stations,1neans for connecting one of said lines to said trunk, signaling devices at the second station, one for each of said lines, and a circuit arrangement involving a lVheatstone bridge or which two ai ins are fixedfresistances, the third arm of which bridge includes one conductor ofthe two wiretrunk and a resistance varied according to which line is connected to the'trunk, and

the fourth arm of which includes the other trunk conductor and a resistance automatically varied until a balance is reached where upon the signaling device corresponding to the line connected to said trunk is operated. 8. In a signaling system, a plurality of lines, a station where-in said lines terminate, a second station, a trunk circuit interconnecting said stations, means for connecting one of said lines to said trunk, sig naling devices at the second station, one for each of said lines, and a circuit arrangement involving a VVhe-atstone bridge of which two of the arms are fixed resistances, the third arm a resistance varied according to which line is connected to the trunk, and the fourth arm a variable resistance, and means including a series of counting relays for automatically' varying the resistance of said fourth arm until a'balance is reached whereupon the signaling device corresponding to the line connected to said trunk is operated.

'9. In a signaling system, a plurality of lines. a station wherein said linesterminate, a second station, a trunk consisting oftwo metallic conductors only interconnecting said stations, means automatically operated when one o1 said lines is taken for use to connect the same to said trunk, arelay (201) associated with said trunk at said second station, a signal controlled thereby, and a circuit for said relay including one side of saidtrunk, a relay (102) operated upon the taking of said line for use for closing. said circuit, means for dee-nergizing said relay (102) upon the extension of the line to the trunk, a cord circuit adapted to be connected to said line and thereby to said trunk, a WVheatstone bridge includinga voltmeter relay (128, 131), a circuit closed by the connection of the cord circuit to the line for applying current to the lVheatstone bridge, and a relay (22) in the cord circuit operated by the closure of the line circuit to apply current to one of the arms of the bridge to unbalancethe same to operate the voltmeter relay to cause the same to provide a substitute energizing circuit for said relay 201).

10. In a service observing system, a plurality of lines, a station wherein said lines terminate, a second station, a trunk consisting of two metallic conductors only interconnecting said stations, switching means at said second station associated with said trunk, means automatically operated when one of said lines is taken for use to connect the same to said trunk, relays (208) and (230) in series with each other and associated with said trunk, asignal (210) controlled by one of said relays (208), a cord circuit adapted to be connected to said line, an operating circuit for said relays (208) and (230) including one side of said trunk, and means actuated by the connection of said cord circuit to said line when said switching means is actuated for closing said circuit, a meter 'for the line, a key in said cord circuit for operating said meter, means controlled by the operation of the meter for opening the circuit of one of said relays (230), and a signal actuated by the release of said relay.

11. In a service observing system, a plu- "ality of lines, a station wherein said lines terminate, a second station, a trunk consisting of two metallic conductors only interconnecting said stations, switching means at said second station associated with said trunk, means automatically operated when one of said lines is taken for use to connect the same to said trunk, a marginal relay (208) associated with said trunk, a relay (230) associated with said trunk and operated upon the actuation of said switching means, a signal (210) controlled by said marginal relay (208), a cord circuit adapted to be connected to said line, an operating circuit for said relays (208) and(230) in cluding one side of said trunk, a circuit including a relay (117) and a marginal relay (118) closed by the connection of said cord circuit to said line, the operation of said relay (117) causing the operation of relay (208) to actuate said signal (210), a meter for said line having a high and a low resistance winding, a key in said cor-d circuit, for operating said meter, means actuated by the operation of the meter for short circuiting its high resistance winding to operate said second mentioned marginal relay (118), and means actuated by the operation of relay (118) for opening the circuit including said trunk to release relay (230), and a signal actuated by the release of relay (230).

12. In a signaling system, a plurality of lines, a station wherein said lines terminate, a second station, a trunk circuit consisting of two metallic conductors only interconnecting said stations, means automatically actuated when one of said lines istaken for use to connect the same with said trunk, signaling devices at the second station, one for. each of said lines, a circuit arrangement adapted to cause the operation of the signaling device corresponding to the line connectedv to the trunk circuit, and a circuit controlled from said second station and including said two trunk conductors in parallel for disconnecting said line from said trunk.

13. In a signaling system, a plurality of lines, a station wherein said lines terminate, a second station, a trunk circuit intercon necting said stations, means automatically actuated when one of said lines is taken for use to connect the same with said trunk, signaling devices at the second station, one for each of said lines a circuit arrangement adapted to cause the operation of the signaling device corresponding to the line connected to the trunk circuit, a polarized relay, and a circuit controlled from said second station and including said polarized relay for disconnecting said line from said trunk.

14. In a signaling system, a plurality of lines, a station wherein said lines terminate, a second station, a trunk circuit consisting of two conductors only interconnecting said stations, means auton'iatically actuated when one of said lines is taken for use to connect the same with said trunk, signaling devices at the second station, one for each of said lines, a circuit arrangement adapted to cause the operation of the signaling: device corresponl cir' .t, a polarized relay, and a circuit con trolled from said second stationincluding said two conductor trunk and said polarind relay for discomiccting trunk.

15. In a signaling system, a plurality of groups of lines, each terminating in a centralstation, a second station, a trunk consisting o't' two conductors only interconnecting: each central station with said second station, means automatically operated when one of the lines is taken for use for connecting the same to the corresponding trunk, signaling devices at the second station common to said trunks, one device for each of said lines, means at the second station controlled hy the operator thereat for associatsa-id devices with one of said trunks, and a circuit arrangement adapted to cause the operationotthe signaling device corresponding to the line connected to the trunk circuit= 16. In a signaling; system, a plurality of ,aroups of lines, eachterminating in a central station, a second station, a trunk interconnecting; each central station with said second station, means automatically operated when one of the lines is taken for use for connecting t l devices at the second station conin. to said trunks, one device for each of said lines, means at the second station controlled by the operator thereat for associating); said devices with one of said trunks, and a cir cuit arrangement involving a Viheatstone Bridge adapted to cause the operation of the signaling device corresponding to the line connected to the trunk circuit.

In a signaling system. a plurality of s, resistances associated therewith, a sta- "ion wherein said lines terminate, a second ing' to theline connected tothe trunk said. line from said he same to the corresponding trunk,

station, a variable resistancethereat, a trunk circuit lnterconnect ng said stations, means for automatically connectinganyone of said lines to said trunk upon the initiation of a call thereon, signaling devices at the second station, one for each of saidlines, and a circuit having parallel paths, one including a portion of said trunk and the resistance associated with said line, and another i11- cluding a portion of'saidtrunk and said variable resistance, means for varying said trunlgsignaling devices at the second stia tion, one for each of said lines,and a circuit having parallelpaths, one including a per tion ofsaid trunk and the resistance associated with said line, and another including a portion of said trunk and said variable resistance, means for varying said latterresi'stance until theresistances of said paths are equalized, and means for thereupon operas ing, the signal devices corresponding to the line connected to said trunk.

19. In a service observing system,.;a p'lurality of lines, resistances associated therewith, station wherein said lines term nate, a second station, a varlable resistance thereat, a trunk consisting of two conductors only interconnecting S2L1'Cl, Si3at1011S, means for automatically connecting any one of; said lines to said trunk uponthe initiation of a. call thereon, signaling devices at the secondjstation, one for each of said lines-and a circuit having parallel paths, one including one side of said trunk and the resistance asso ciated with the lineconnected to the trunk, and the other including the other side of said trunk and said variable resistance,

means for varying; said latter resistance until the, resistances of said paths are equalized, and means for thereupon operating the signal device corresponding to the line connects,

ed to said trunk.

In witness whereof, I hereunto subscribe my name this 3rd day of October A. 1)., 1921. i

ROY DQ CONVAY. 

